When I was young I also was pretty good at these interviews and loved doing coding contests and such for fun. However when I joined a big company I learned what really is hard about software "engineering".
It's dealing with legacy code, finding and fixing bugs in highly distributed systems, understanding tickets from customers, managing integration of different components, balancing tests to be enough but not to be too much.
In general the hard tasks are very rarely one specific well determined problem such as finding a node in a tree in the most performant way.